Though I think plot is important, I tend to put the characters first in my comics, as it is usually what the readers (at least me, as a reader) relate to and get attached to. I think having lovable, funny or charismatic characters is what hooks the readers at first, and then they continue reading if the plot is as good as the characters.
I also think the characters' strength is how they evolve, so of course, if the plot is non-existent, the characters can't evolve, or they might look blend, hence I do think the plot is very important as well.
But that's only my way of seeing it! Others artists or readers might see it completely differently. I'm sure if the plot is excellent, the characters will naturally shine anyway.
And I totally agree with @djourner !